The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
Two control system types have been developed for multiple speed automatic transmissions for motor vehicles and dominate this field. A first type utilizes pressurized hydraulic fluid (transmission oil) provided to a control valve body having a plurality of multi-port spool valves which direct such fluid to a plurality of hydraulic actuators which control clutches and brakes associated with various elements of a plurality of planetary gear assemblies. Such a transmission may be essentially self-contained as most upshift and downshift decisions are made by the valves in the control valve body.
A second type of control system, more recently developed, utilizes solenoid valves and multiple port spool or logic valves to direct pressurized hydraulic (transmission) fluid to a plurality of actuators associated with synchronizer clutches and one or two drive gears. Activation of a solenoid valve when the spool or logic valves are appropriately positioned, provides hydraulic fluid which translates an actuator and engages a desired gear and speed ratio. This type of control system is particularly suitable for use with dual clutch transmissions (DOT's).
In the past, both of these control systems typically are optimized for certain performance or operational features such as fuel economy or exceedingly smooth shifts. The present hydraulic control system provides numerous features previously not found in a single control system and is optimized for many of them.